2.0 Analysis 2.1 Introduction The separation of the off-wing slide during the approach into Vancouver was caused by an undetected maintenance error as a result of a series of actions and inactions that took place in Toronto prior to the departure of flight 899. The analysis examines how these events interacted to culminate in a potentially dangerous in-flight incident. 2.2 Restoration of the Off-Wing Slide System The breakdown in acceptable and standard maintenance practices began when the inflation bottle was disconnected with no formal record made of the fact to ensure that the bottle was reactivated before the aircraft was released for service. Continuity was lost when the morning-shift technician who had been briefed about the disconnection was subsequently assigned to work on another aircraft. Contributing to the consequence of this error was the lack of requirement for an adequate inspection of the area before the access panel was reinstalled. The aircraft was eventually dispatched on flight 899 in an unsafe condition: the right off-wing slide was inoperative and would not have been available had an emergency required the evacuation of the occupants through the right over-wing exits. From the standpoint of the in-flight opening of the off-wing slide compartment, the more significant deviation began when the morning-shift certified aircraft technician did not install a new shear pin in the secondary lock, as required by the job ticket. Had the technician understood the operation of the off-wing slide system, he would have realized that the shear pin had to have been sheared during the inadvertent actuation and, therefore, replacement of the shear pin was mandatory. Even though the presence of the sheared shear pin fragments in position on the integrator gave the false impression that the pin was intact, the morning-shift technician's decision not to replace the shear pin as required was influenced primarily by the lack of a replacement close at hand. Since the aircraft was already late, pressure to expedite the release of the aircraft possibly influenced the technician in his decision to certify on the job ticket that the shear pin had been replaced when it had not. The shear pin problem would have been detected had the integrator been manually cycled, as called for by the 767 airplane Maintenance Manual procedures for replacement of the latch actuator. 2.3 Door Warning Inspection The certified aircraft technician who was sent on the ramp to inspect the right off-wing slide compartment door had virtually no experience with this system and had retained limited knowledge of it from his endorsement course four years previously. The technician's unfamiliarity with the slide system and the history of inadvertent deployments reinforced his apprehension about handling anything associated with the slides for fear of an inadvertent deployment that might result in personal injury and equipment damage, or delays in aircraft operations. As a result, the inspection on the ramp was cursory and inadequate to ensure that the door warning was false, the premise under which the aircraft was released. 2.4 Minimum Equipment List Inspection Requirements Although the ramp technician and the ramp maintenance supervisor knew that a detailed inspection was mandatory before the aircraft could be released, this inspection was not done. The complete actuation of the integrator as called for in the MEL inspection would have allowed detection of the sheared pin. The fact that maintenance activity had just taken place on the slide system should have raised greater concern about a potential problem. However, the MEL inspection was not followed; instead, an informal procedure was conducted which allowed the sheared condition of the pin to remain undetected. Although the flight crew had no knowledge that the MEL inspection requirements were not carried out by maintenance, they did know that the requirement to placard the warning light and make a log-book entry was not met. They accepted the aircraft as airworthy based on a verbal release from maintenance, which again was a deviation from the required formal procedures. 2.5 Door Warning and Opening The sheared shear pin allowed the secondary lock latch lever to rotate out of position and the latch shaft to migrate out of position towards the unlatched position, likely due to vibration. At the first movement, the proximity switches that monitor the system triggered the warning lights and the EICAS message during de-icing of the aircraft prior to departure. The warnings temporarily disappeared when the ramp technician handled the system during inspection, but the primary cause was not resolved. Some of the previous incidents of off-wing slide compartment door opening in flight occurred during approach. It is likely that the off-wing compartment door became unlocked due to vibration and opened due to aerodynamic and inertial loads during approach. The slide did not inflate, but simply unfurled and tore away. 3.0 Conclusions 3.1 Findings The right off-wing slide compartment door and spoiler squib were inadvertently activated during the return-to-normal procedure after an A check. The right off-wing slide inflation trigger was disconnected during the actuator replacement, and was unintentionally not reconnected. Because the inflation cylinder was disconnected, the right off-wing slide was unserviceable for flight 899. The shear pin in the secondary lock sheared during the inadvertent actuation, and was not replaced during restoration of the system as required by the job ticket. The sheared condition of the pin allowed the latch shaft to migrate to the unlatched position, likely as a result of vibration. In response to the door warning light and the EICAS alert message, an informal inspection, which did not include the items listed for the MEL inspection, was done on the right off-wing slide compartment door. The sheared condition of the pin remained undetected as a result of the MEL inspection not being completed. The aircraft was released for the flight under the authority of the MEL, even though the MEL inspection had not been completed. The flight crew accepted the aircraft without the required placard and log-book entry. The maintenance personnel who were directly involved with this incident had inadequate experience and knowledge of the system. 3.2 Causes The right off-wing slide compartment door opened in flight because the secondary lock shear-pin had been inadvertently sheared during recent inspection; this maintenance error remained undetected because existing required inspection procedures had not been followed. Contributing to the deviations from formal standard practices was inadequate understanding of the system on the part of the maintenance technicians and supervisor. 4.0 Safety Action 4.1 Action Taken 4.1.1 Action by the Operator Subsequent to this occurrence, Air Canada took the following actions: to confirm the integrity of the secondary lock shear pin, the MEL was revised to require turning one end of the pin while observing the other end; also, a once-around check is underway to ensure that five spare shear pins are stowed at the integrator on each side of the aircraft; A Check Job Tickets were changed so that the off-wing door is no longer deactivated during an A Check and a warning sign is placed over the interior of the door to reduce the possibility of inadvertent over-wing slide deployment; and maintenance procedures for the door indication system were revised, and two projects are in the approval process (Service Bulletin (SB) 25A0131 to replace the integrator, and SB 25-0212 to improve the off-wing slide arm/disarm mechanism). 4.1.2 Action by Aircraft Manufacturer Boeing has released Service Bulletins 767-25-0051, 767-25A0104, and 767-25-0185 to provide more direct verification of slide door latching, and to improve the integrator locking and latching mechanism.